Water jet propulsion unit

ABSTRACT

A water jet propulsion unit including two deflector blades which are located in the pressurized water stream emanating from a rotatable impeller and being movable about respective pivots by steering means so as to deflect the water stream to give directional control to an associated craft. The blades are moved in the same directin of rotation by the sterring means so as to emanate a parallel relationship. Actuating means are also connected to the blades and are operative to move the blades in opposite directions about their pivots so as to locate them in a position such as to direct the stream of water forwardly of the craft and thereby create rearward propulsion. The impeller is mounted in the housing which also carries the deflector blades and is arranged for attachment to the outside of the rear wall of the craft, and water is fed into that housing through a tunnel member secured within the craft and extending between the rear and bottom walls thereof.

United States Patent r1 1 Macardy et al.

[1 1' 3,824,946 51 July 23,1974

1 1 WATER JET PROPULSION UNIT [76] Inventors: Douglas Macardy; IanWilliam Kelly, both of 75 Beverly St. East Doncaster, Victoria,Australia 221 Filed: Aug. 30, 1972 21 Appl. No.: 284,913

[52] US. Cl 115/12 R [51] Int. Cl B63h 11/10 [58] Field of Search115/11, 12 R, 13, 14, 35 R; 244/83 B;114/151,152,163, 164;

[56] References Cited UNITED STATES PATENTS 1,670,622 5/1928 Hickman114/145 R 2,460,374 2/1949 Walls 244/83 B 3,187,708 6/1965 FOX 115/12 R3,283,737 l1/1966 Gongwer 115/12 3,561,392 2/1971 Baez 115/12 R3,570,247 9/1969 Denning 61 al. 60/230 Z I UM Primary Examiner-Duane A.Reger Assistant Examiner-Jesus D. Sotelo Attorney, Agent, or Firm-Lerner, David, Littenb r i sr m [5 7 ABSTRACT A water jet propulsionunit including two deflector blades which are located in the pressurizedwater stream emanating from a rotatable impeller and being movable aboutrespective pivots by steering means so as to deflect the water stream togive directional control to an associated craft. The blades are moved inthe same directin of rotation by the sterring means so as to emanate aparallel relationship. Actuating means are also connected to the bladesand are operative to move the blades in opposite directions about theirpivots so as to locate them in a position such as to direct the streamof water forwardly of the craft and thereby create rearward propulsion.The impeller is mounted in the housing which also carries the-deflectorblades and is arranged for attachment to the outside of the rear wall ofthe craft, and water is fed into that hous- 8 Claims, 12 Drawing Figures1 WATER JET PROPULSION UNIT This invention relates to water jetpropulsion units of the kind used in boats and other marine craft. Forconvenience, the invention will be hereinafter described in relation toboats, but it will be appreciated that the invention is applicable toother marine or water-borne craft not generally designated as boats.

Water jet propulsion units generally include an openended tunnel whichis arranged to be mounted in a boat so that the opposite ends thereofopen through the base and stem of the boat respectively. Means isprovided within the tunnel to draw water through the base opening,pressurize that water and discharge it through the stern opening as apressurized stream or jet. The reaction between the stream or jet andthe body of water supporting the boat, provides the propulsion effect.

The pressurizing means usually includes at least one impeller, and thesection of the tunnel containing that impeller must be relativelystraight so as to enable mounting of the impeller and minimize fluidleakage radially of the impeller, and also must be formed of arelatively hard material such as metal in order to keep wear withinacceptable limits and obtain a reasonable operational life. As theimpeller is generally mounted intermediate the length of the tunnel, theentire tunnel is usually made of metal. Because of the foregoingrequirements, manufacture of the tunnel is complex and expensive,accurate mounting of the tunnel is difflcult, and maintenance iscomplicated by the location of the impeller.

A further disadvantage of prior constructions is that directionalcontrol of the jet is normally effected by a nozzle or similar deflectorwhich at least partially surrounds the ejected stream of water and ispivotally mounted so as to enable the direction of that stream to bechanged. Such an arrangement is rather complicated, and the nozzle isdifficult to turn because the contained stream always tends toreturn thenozzle to its neutral position. In addition, that arrangement makes itdifficult to incorporatemeans whereby reverse movement of the boat canbe effected. Such reversing means normally includes a pivotal shroud orchute, and is complicated even under favourable circumstances. a

It is a principal object ofthe present invention to provide a propulsionunit of the kind indicated which is re]- atively simple and economic inconstruction and presents minimum difficulties in mounting within aboat. A further object of the invention in a preferred form is toprovide such a unit which requires comparatively little effort to effecta change in direction, and which is able to effect reverse movement ofthe associated boat.

According to one aspect of the present invention, there is provided awater jet propulsion unit including, an open-ended tunnel arranged to besecured to a boat or other water-borne craft, a housing formed separatefrom and releasably securable across or to a rear end of said tunnel soas to receive water from said tunnel, and water pressurizing meansmounted within said housing.

According to a further aspect of the invention, there is provided awaterjet propulsion unit including, an open ended tunnel arranged to besecured to a boat or other water-borne craft, an impeller rotatablymounted at or adjacent a rear end of said tunnel and operative topressurize water passing through or received from said tunnel andproject same towards an outlet opening of said unit, at least onedeflector blade pivotally mounted at or adjacent said opening formovement between an open position in which it does not substantiallyaffect the direction of emergence of said pressurized water from saidopening, and a closed position in which it substantially prevents, or itcooperates with a further said blade or blades to substantially prevent,passage of said pressurized water through said opening, and steeringmeans for moving said blade about its pivot through a range of steeringpositions in which the blade is operable to deflect said pressurizedwater and thereby control the direction of emergence of same from saidopening.

In a preferred form of the invention two blades are provided with theirpivotal axes on opposite sides respectively of the centre of the outletopening, and steering means is connected to both said blades andoperative to cause the blades to move in the same direction of rotationand maintain them substantially parallel in their steering positions. Itis further preferred that an actuator or selector be connected to theblades so as to enable rapid movement of same between their open andclosed positions, and that actuator is preferably arranged so as tocause the blades to move in opposite directions of rotation.

The following description refers in more detail to these essentialfeatures and further optional features of the invention. To facilitatean understanding of the invention, reference is made to the accompanyingdrawings where these features are illustrated in preferred form. It isto be understood however, that the essential and optional features ofthe invention are not limited to the specific forms of these features asshown in the drawings.

In the drawings:

FIG. 1 is a side elevational view of one particular jet propulsion unitmade in accordance with the invention, parts being broken away forconvenience of illustration;

FIG. 2 is a transverse cross-sectional view taken along line IIII ofFIG. 1;

FIG. 3 is-a plan view looking in the direction of arrows III-III of FIG.1, and showing the deflector blades in the open position;

FIG. 4 shows the blades in the same position as FIG. 3, but part of theactuator mechanism has been omitted to show the interconnection betweenthe blades;

FIG. 5 is a view similar to FIG. 3 but showing the blades located in aselected steering position;

FIG. 6 shows the blades in the same position as FIG. 5, but part of theactuator mechanism has been omitted to show the connection between theblades;

FIG. 7 is a view similar to FIG. 3, but showing the actuator at aposition intermediate the forward drive and reverse drive positions;

FIG. 8 is a view similar to FIG. 7 but showing the actuator moved fullyin the reversed drive position;

FIG. 9 is a cross-sectional view taken along line IX-IX of FIG. 8;

FIG. 10 is a view similar to FIG. 8 but showing the steering mechanismoperated to cause slight opening of one deflector blade;

FIG. 11 is an end elevational unit looking in the direction of arrowsXIXI of FIG. 1; and

, FIG. 12 is a longitudinal sectional view of part of the housingshowing pump or water cooling connections.

in FIG. 1 and includes the usual open-ended tunnel 2 arranged to providea communication between openin gs in the base 3 and rear wall ortransom-4 of a boat. In contradistinction to prior units however, thepressurizing means 5 is not located within the body of the tunnel 2 sothat the tunnel 2 can be manufactured with less concern for tolerancesand wear-resistance. With regard to the last point, the pressurizingmeans 5 is located rearwardly of the stem end 6 of the tunnel 2 so thatin use the tunnel 2 is subjected to lower internal pressure than is thecase in prior constructions. Because of this novel arrangement thetunnel 2 can be manufactured of fiberglass, other reinforced plasticsmaterials, or any other relatively inexpensive and easily workablematerial having sufficient rigidity to support the working pressures towhich the tunnel 2 will be subjected.

Mounting of the tunnel 2 within a boat isgreatly simplified with thisconstruction since it is much easier to cut and shape the ends of thetunnel 2 to suit a particular boat. In addition, a tunnel 2 made of aplastics material can be easily bonded in place so as to form anintegral part of the boat.

Yet another advantage arising out of this novel tunnel construction isthat it does not require a straight section to contain the pressurizingmeans, and consequently water within the tunnel 2 is not subjected tosudden changes in direction. The longitudinal axis of j the tunnel 2 canbe formed as part of a circle, or it may follow the path of severalmerging arcs, or any other suitable path suchas to'effect desirable flowcharacteristics within the tunnel 2. Cavitation problems may beminimized by forming the tunnel 2 so that it gradually increases indiameter (the tunnel is usually circular in cross-sectional shape)towards the stern end 6, whereas the reverse generally applies in priorconstructions, and such an increase need only be affected over an endportion of the tunnel as distinct from the entire length thereof.

As previously mentioned, the pressurizing means 5 is located rearwardlyof the stem end 6 of the tunnel 2, andin the preferred constructionshown it is arranged to bemounted externally of therear wall ortransom'4 of a boat so as to facilitate maintenance. In the constructionshown, the pressurizing means includes an impeller 7 which is rotatablymounted within a housing 8.

, The impeller 7 may be of any suitable construction to produce asatisfactory pressure gradient, and if desired more than one impellercan be used. The housing 8 can be formed of metal or otherwear-resistant material and is preferably arranged as shown to be boltedor otherwise releasably secured to the stern wall or transom 4 of aboat. As shown, the tunnel 2 and housing 8 cooperate through a spigot 9and recess ll-provided on the stem end 6 of the tunnel 2 and the housing8 respectively, so as to enable convenient and accurate location of theimpeller housing 8 relative to the tunnel 2.

Drivemeans for the impeller may take any appropriate form, but in thepreferred embodiment shown includes an internal combustion orcompression ignition engine (not shown) having a drive shaft 12 which,in the assembled condition of the unit, connects with a further shaft 13through an appropriate universal joint or coupling 14, which shaft 13extends through a bearing part 15 of the tunnel 2 and has the impeller 7mounted thereon. The impeller 7 is screwed or otherwise secured to theshaft 13 so as to rotate therewith, and an end portion 16 of the shaft13 is rotatably supported within a bearing 17 secured to the housing 8as hereinafter described. If desired that bearing may be located withina separately formed rear extension which is removably attached to thehousing 8.

Water straightening vanes 18 are located directly behind the impeller 7of the preferred embodiment shown to ensure that a maximum thrust effectis obtained from the pressurized stream of water emanating from theimpeller 7. The vanes 18 may be of any known construction and as shownin FIGS. 1 and 2, are preferably secured within the impeller housing 8so as to extend between the bearing 17 and the housing wall, and therebyprovide a support for the bearing 17.

In the preferred construction shown, means is provided to form thepressurized stream so that it is substantially annular in transversecross-section at the zone of ejection from the unit. Such means includesa cone or cone-like member 19 which is secured to the impeller housing 8and is arranged to diverse rearwardly as shown in FIG. 1. Part of theimpeller housing 8 surrounds the cone member 19 in radially spacedrelationship so as to define an annular discharge orifice 21, which ismore clearly shown in FIG. 9. In the form shown, the cone member 19provides a hub or boss for the water straightening vanes 18, and alsocontains the rear bearing 17 for the shaft 13, which bearing can bewater lubricated. I

Steering of a boat powered by a unit according to the invention may beeffected through a conventional rudder system, but in the preferredembodiment illustrated, the unit incorporates its own directionalcontrol means whereby the direction of emergence of the pressurizedstream or jet can be regulated. Such control means preferably includesat least one blade located in the path of the merging stream and mountedfor pivotal movement about an upright axis. The blade acts as adeflector when disposed angularly relative to the normal direction ofemergence of the pressurized stream, and may be arranged to enabledeflection of the stream through substantially l and thereby causereverse movement of the associated boat. Ideally, the blade is elongatedin the direction of its pivotal axis.

In the preferred construction shown, two deflector blades 22 and 23 areprovided, although a greater number can be used if desired, and theblades are pivotally mounted at 24 and 25 respectively (see FIG. 5) on ashroud element 26 projecting rearwardly of the impeller housing 8. Theblades 22 and 23 are mounted with their pivotal axes on opposite sidesrespectively of the centre of the annular discharge orifice 21, and theleading and trailing edges of each blade may be spaced a substantiallyequal distance from their respective pivot axes for a reason hereinaftermade clear. Also, each pivotal axis 24- and 25 is preferably laterallyspaced from the centre of the discharge orifice 21 by a distancesubstantially equal to the distance between that axis and the leading ortrailing edge of the associated deflector blade.

The blades 22 and 23 are arranged and formed to be capable of closingthe outlet end of the shroud 26 so as to effectively bar discharge ofthe pressurized stream rearwardly of the shroud 26. In practice someleakage may occur through that barrier, but the bulk of the stream willbe deflected back towards the bow of the associated boat. The forwardlydeflected stream escapes from the'housing 8 through at least one opening27 (see FIGS. 1, 2 and 9) defined between a front end portion of theshroud 26 and apart of the body of housing 8 located within that frontend portion, but the openings 27 may be formed by any other suitablearrangement. For best results the'escape openings 27 are locatedforwardly of the main discharge orifice 21.

Movement of the deflector blades may be effected through any appropriatesteering means, and in the preferred form shown that means includes arack and pinion assembly. The rack 28 is mounted to slide within guides(not shown) and is operatively connected to each blade 22 and 23 so thatthe pivotal position of each blade is determined by the position of therack 28 within its guides. Linear movement of the rack 28 is effected byrotation of the cooperating pinion 29 which may be connected by means ofa shaft 31 to a wheel, handle, or other manually operable device (notshown). The arrangementis preferably such that both blades 22 and 23move in unison and always have the same position relative to the normaldirection of discharge of the pressurized stream i.e., they are retainedsubstantially parallel.

In the particular form of the invention illustrated, the rack 28 isoperatively connected to the deflector blades 22and 23 through opposedabutment surfaces 32 on the rack 28, each of which abutment surfaces 32is engageable with a cooperable element attached to a respective oneofthe blades 22 and 23. The abutment surfaces 32 are formed onrearwardly directed projections 33 provided at each end of the rack 28,and each cooperable element is formedby an extension of a pivot pin 34(see FIG. 11) associated with the respective deflector blade 22 or 23.Each pin 34 is connected to an end portion of a respective arm 35, oneof which is secured to the pivot spindle 24 and the other is secured tothe pivot spindle 25. Thus, the arms 35 move links 36, which for thisparticular arrangement is formed by the pivot pin connecting the links36. The link pivot pin 42 has its axis substantially parallel to thepivotal axes of the deflector blades 22 and 23, and if desired a rollermay be mounted on that pin for engage with the blades 22 and23, andthose arms are arranged so that the extensions of pins 34 are disposedbetween the opposedabutment surfaces32 of the rack 28. The arms 35 areconnected at their outer ends by two pivotally connected links36 so thatmovement of one arm 35 causes corresponding movement of the other, andconsequently the associated blade. That is, each arm 35 is pivotally.connected by one of the pins 34 to an end portion of a respective one ofthe links 36.

Adjusting means may be provided to enable variation I of the amount offree movement of the rack relative to the blade arms. In an arrangementnot shown, such means may include an adjusting screw threadably mountedin the outer end portion of each arm and pro jec'ting therethrough sothat a conical nose section of the screw depends from the arm and isengageable by the adjacent abutment surface of the rack. Each suchabutment surface may be provided with a slope correspondingsubstantially to the taper of the aforementioned nose section, and themaximum clearance between each nose section and associated abutmentsurface is determined by the axial position of the screw rel ative toits arm.

The steering means described above may be used to turn the blades 22 and23 into the position in which they close the shroud outlet and causereverse movement of the associated boat. It is preferred however,

that a separate reverse actuator is provided to enable positive andrapid movement of the blades into their reverse position. One suchactuator, as shown in the ment with the cam surfaces 41. The camsurfaces 41 are arranged so that longitudinal movement of the actuatorrod 37 in a rearward direction (or a forward direction if preferred)causes the links 36 to collapse (see FIGS. 7, 8 and 10) about thecentral pivot 42 so that the two links 36 swing inwardly towards eachother. Such relative movement of the links 36 causes the deflectorblades 22 and 23 to move about their respective pivots 24 and 25, andrelatively little movement of the actuator rod 37 is required to bringthe blades 22 and 23 into a position in which they effectively close theshroud outlet as shown in FIG 8. A handle or other manually operablemeans (not shown) may be attached to the forward end of the rod 37 tofacilitate operation thereof.

In the normal or forward position of the actuator rod 37, the plate 38is arranged so that the two links 36 are retained in substantialalignmentas shown inFIG. 4 so that thelinks 36 functions as a singlerigid body. Each cam surface 41 is shaped to retain the links 36 in thatposition as the rack 28 and links 36 are moved endwise during steeringoperations. It will beappreciated however, that the actuator rod 37 canbe moved to place the deflector blades 22 and 23 in their reverseposition, regardless of the steering position oflthe rack 28 and links36. Furthermore, when the deflector blades 22 and 23 are in the reverseor closedposition it is preferred that they are disengaged from thesteering means, and that may be achieved by having the blade arms 35located so that the pins 34 are not engageable by the rack abutmentsurfaces 32, as shown in FIG. 10.

Steering during reverse operation of the unit may be effected in anyappropriate manner, and according to the preferred arrangement therearward projections 33 associated with the rack 28 each have a camsurface 43 which is cooperable with a cam surface 44 formed on theadjacent steering arm 35. The arrangement is such that, when the baldes22 and 23 are in the closed position as shown in FIG. 8, each camsurface 44 is engageable by the adjacent cam surface 43 when the rack 28is moved endwise in either of the two directions allowed by itsassociated guide. FIG. 10 shows the rack 28 moved in one direction sothat the cam surfaces 43 and 44 shown at the lower part of the figureengage and cause the blade 23 to be moved slighty towards the openposition such as to allow lateral escape of water from the housing 8.That lateral discharge will have a steering effect on the unit, and itwill be appreciated that either blade 22 or 23 may be manipulated inthis way to effect a desired direction of steering.

In an alternative arrangement not shown, a steering nozzle may beoperatively connected to the reversing mechanism described. Preferably,two such nozzles are provided at the front region of the shroud onopposite 7 sides thereof,and each may extend laterallyfrom an upstandingreceiver tube rotatably mounted in the shroud or some other part of theunit. Each receiver tube has a slot or other shaped port formed thereinwhich communicates with the or a respective escape openingof the shroudwhen the reverse mechanism is positioned to locate the deflector blades22 and 23 across the rear outlet of the shroud 26. The receiver tubesare also operatively connected to the steering means, at least in thereverse position of the actuator rod 37, so that steering is effectedthrough movement of the rack which causes rotation of the receiver tubeswith consequent change in the direction of discharge of the nozzles.

If desired, the nozzles may remain connected to the steering means inall positions of the actuator rod so that they extend rearwardly whenthe deflector blades are positioned for normal forward movement.

Retaining means (not shown) such as a springloaded ball detent andcooperable recesses, may be provided 'to releasably retain the actuatorrod 37 in its forward,

neutral. and reverse movement positions. Preferably, the deflectorblades 22 and 23 are operatively connected to the steering means in theforward position only of the actuator rod 37, which is shown in FIGS. 3to 6. In the netural position of the rod 37 (shown in FIG. 7) the blades22 and 23 are positioned so that they deflect the ejected water streamlaterally in substantially opposite directions so that each part of theejected stream counteracts the other, and the precise location of theneutral position may vary with conditionsof use. In the neutralposition, there is little or no tendency for the unit to drive anassociated boat in a forward or reverse direction.

A cover (not shown) of reinforced plastics or other suitable materialmay be located over the steering and reverse mechanisms for protectionof same, and provision is made to allow easy removal of that cover formaintenance purposes. I

When a unit according to the invention is mounted on a boat, it ispreferably arranged so that the normal direction of discharge of thepressurized stream is in substantial'alignment with the longitudinalaxis of the boat. Thus, the boat is caused to follow a straight line inthe forward direction when thecontrol blades 22 and 23 have theirdeflection surfaces, which are preferably flat, arranged parallel tothenormal direction of discharge. When it is desired to turn the boat, theblades 22 and 23 are moved through an appropriate angle (FIGS. 5 and 6)by means of the steering mechanism and such movement encounters minimumresistance by the pressurized stream because that stream impingesagainst substantially equal areas of each blade 22 and 23 on both sidesof the respective blade pivot. Thus, the forces acting on each blade 22and 23 are substantially balanced in all blade positions.

Reverse movement of the boat can be rapidly effected by pushing theactuator rod 37 into its reverse position as shown in FIGS. 8 and 9, andin that position the outlet of the shroud 26 is completely closed.Steering of the boat when reversing is effected by moving the rack 28into a position such that one of the cam surfaces 44 engages itsadjacent cam 43 and thereby cause opening movement of the associatedblade 22 or 23. Such movement does not detract significantly from thereverse drive force of the unit, but permits a lateral discharge asshown in FIG. 10, which is sufficient for steering.

. It will be appreciated that a propulsion unit as described possessesnumerous advantages over prior water jet units. The advantages arisingout of the particular tunnel and impeller housing arrangement havealready been discussed. Another important advantage is that reversemovement of an associated boat can be effected in a simple and positivemanner. Still further, the use of an annular discharge orifice permitsthe size of the unit to be condensed and also enables production oflower discharge velocities and a greater volume in the pressurizedstream ejected by the unit. Reduction in size of the unit as comparedwith prior constructions permits the use of heavy materials such asbronze, for the impeller housing without resulting in an excessivelyheavy unit.

Finally, it is to be understood that various alterations, modificationsand/or additions may be introduced into the constructions andarrangements of parts previously described without departing from thespirit or ambit of the invention.

Having now described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. A water jet propulsion unit including an open- I ended tunnelarranged to be secured to a water-borne craft; an impellerrotatablymounted adjacent a rear end of said tunnel, operative to pressurizewater passing through or received from said tunnel and project sametowards an outlet opening of said unit; two deflector blades pivotallymounted adjacent said opening for movement between an open position inwhich they do not substantially effect the direction of emergence ofsaid pressurized water from said opening, and a closed position inwhichthey-cooperate with each other to substantially prevent passage ofsaid pressurized water through said opening; steering means for movingsaid blades about their respective pivots in the same direction ofrotation through a range of steering positions in which each said blade.is operable to deflect said pressurized water and thereby control thedirection of emergence of same from said opening; said blades beingmounted in side-by-side relationship and each having its pivotal axislocated so thatin a said steering position said pressurized waterimpinges on each of two sections of the said blade which are disposed onrespective opposite sides of said axis; and an actuator is connected tosaid blades and is operable to move them between said open and closedpositions by causing said blades to simultaneously rotate about theirpivots in "opposite directions respectively.

2. A unit according to claim 1, wherein said actuator includes aslidably mounted rod which is connected to links which interconnect saidblades and are pivotally connected to one another; said actuatorretaining said links against relative movement when in a forward driveposition, and causing relative movement of said links when moved betweensaid forward drive position and 'a reverse drive position.

3. A unit according to claim 2, wherein said steering means includes arack and pinion assembly which is operable to move said blades in thesame direction of rotation and maintain them in substantially parallelrelationship in said steering positions, and said actuator rod isslidably mounted within a shaft to which said pinion is secured.

. tunnel, said reverse drive opening being located forwardly of saidoutlet opening so as to allow escape of said pressurized water from saidunit in one or more streams when each said blade is in the closedposition,

the said reverse drive opening being arranged so that a said streamemerges therefrom in a direction substantially opposite to that in whichwater emerges from said outlet opening when each said blade is in theopen position.

5. A unit according to claim 1, wherein a series of water straighteningvanes are located intemiediate said impeller and said deflector blades.

6. A unit according to claim 5, wherein said vanes extend radiallyoutwards from a conical hub member arranged coaxial with said impellerand diverging away from said impeller, and an annular discharge orificeis defined between the large diameter end of said hub and thesurrounding surface of the housing containing said impeller.

7. A housing for a water jet propulsion unit, said housing being openended and including a forward compartment for receiving an impeller, anoutlet opening defined at a rear end, a conical boss located axially ofsaid housing intermediate said compartment and said outlet opening anddiverging away from said compartment, a series of water straighteningvanes extending radially from said boss and connected to the surroundingwall of said housing, an axial bore formed in said boss for receivingportion of an impeller shaft, and two deflector blades arranged inside-by-side relationship and pivotally connected to said housingadjacent of its pivotal axis and the said axis being located intermediate the longitudinal edges thereof. 8. A water jet propulsion unitincluding, an openended tunnel arranged to be secured to a water-bornecraft; an impeller rotatably mounted adjacent a rear end of said tunneland operative to pressurize water passing through or received from saidtunnel and project same towards an outlet opening of said unit; twodeflector blades pivotally mounted adjacent said opening for movementbetween an open position in which they do not substantially effect thedirection of emergence of said pressurized water from said housing, anda closed position inrwhich they cooperate with each other tosubstantially prevent passage of said pressurized water through saidopening; steering means for moving said blade about their respectivepivots in the selected one of said blades through a limited distancefrom its closed position towards the open position when said actuator isarranged to locate said blades in their closed position, and therebyenable directional control in the reverse condition of said unit.

1. A water jet propulsion unit including an open-ended tunnel arrangedto be secured to a water-borne craft; an impeller rotatably mountedadjacent a rear end of said tunnel, operative to pressurize waterpassing through or received from said tunnel and project same towards anoutlet opening of said unit; two deflector blades pivotally mountedadjacent said opening for movement between an open position in whichthey do not substantially effect the direction of emergence of saidpressurized water from said opening, and a closed position in which theycooperate with each other to substantially prevent passage of saidpressurized water through said opening; steering means for moving saidblades about their respective pivots in the same direction of rotationthrough a range of steering positions in which each said blade isoperable to deflect said pressurized water and therebY control thedirection of emergence of same from said opening; said blades beingmounted in side-by-side relationship and each having its pivotal axislocated so that in a said steering position said pressurized waterimpinges on each of two sections of the said blade which are disposed onrespective opposite sides of said axis; and an actuator is connected tosaid blades and is operable to move them between said open and closedpositions by causing said blades to simultaneously rotate about theirpivots in opposite directions respectively.
 2. A unit according to claim1, wherein said actuator includes a slidably mounted rod which isconnected to links which interconnect said blades and are pivotallyconnected to one another; said actuator retaining said links againstrelative movement when in a forward drive position, and causing relativemovement of said links when moved between said forward drive positionand a reverse drive position.
 3. A unit according to claim 2, whereinsaid steering means includes a rack and pinion assembly which isoperable to move said blades in the same direction of rotation andmaintain them in substantially parallel relationship in said steeringpositions, and said actuator rod is slidably mounted within a shaft towhich said pinion is secured.
 4. A unit according to claim 1, wherein atleast one reverse drive opening is provided in a housing containing saidimpeller and secured to the rear end of said tunnel, said reverse driveopening being located forwardly of said outlet opening so as to allowescape of said pressurized water from said unit in one or more streamswhen each said blade is in the closed position, the said reverse driveopening being arranged so that a said stream emerges therefrom in adirection substantially opposite to that in which water emerges fromsaid outlet opening when each said blade is in the open position.
 5. Aunit according to claim 1, wherein a series of water straightening vanesare located intermediate said impeller and said deflector blades.
 6. Aunit according to claim 5, wherein said vanes extend radially outwardsfrom a conical hub member arranged coaxial with said impeller anddiverging away from said impeller, and an annular discharge orifice isdefined between the large diameter end of said hub and the surroundingsurface of the housing containing said impeller.
 7. A housing for awater jet propulsion unit, said housing being open ended and including aforward compartment for receiving an impeller, an outlet opening definedat a rear end, a conical boss located axially of said housingintermediate said compartment and said outlet opening and diverging awayfrom said compartment, a series of water straightening vanes extendingradially from said boss and connected to the surrounding wall of saidhousing, an axial bore formed in said boss for receiving portion of animpeller shaft, and two deflector blades arranged in side-by-siderelationship and pivotally connected to said housing adjacent saidoutlet opening for movement about respective axes extended transverse tothe longitudinal axis of said housing, each said blade being elongatedin a direction of its pivotal axis and the said axis being locatedintermediate the longitudinal edges thereof.
 8. A water jet propulsionunit including, an open-ended tunnel arranged to be secured to awater-borne craft; an impeller rotatably mounted adjacent a rear end ofsaid tunnel and operative to pressurize water passing through orreceived from said tunnel and project same towards an outlet opening ofsaid unit; two deflector blades pivotally mounted adjacent said openingfor movement between an open position in which they do not substantiallyeffect the direction of emergence of said pressurized water from saidhousing, and a closed position in which they cooperate with each otherto substantially prevent passage of said pressurized water through saidopening; steering means for moving said blade about their respectivepivots in the same direcTion of rotation through a range of steeringpositions in which each said blade is operable to deflect saidpressurized water and thereby control the direction of emergence of samefrom said opening; and an actuator is connected to said blade and isoperable to move them between said open and closed positions by causingsaid blades to simultaneously rotate about their pivots in oppositedirections respectively, said steering means including a cam mechanismoperable to move a selected one of said blades through a limiteddistance from its closed position towards the open position when saidactuator is arranged to locate said blades in their closed position, andthereby enable directional control in the reverse condition of saidunit.